DENVER (AP) - Colorado U.S. Senate hopeful Jon Keyser, once considered a preferred challenger to incumbent Democrat Michael Bennet by national Republican leaders, refused Thursday to answer questions about forged voter signatures on petitions that helped get him on the state GOP primary ballot.

Keyser repeatedly stated, “I’m on the ballot,” when asked at a candidates’ forum about reports that 10 voter signatures had been forged. Keyser did the same when asked by Denver’s KMGH-TV, which reported the forgeries.

Keyser chose to petition his way onto the June 28 ballot and had to go to court to reverse a finding that his campaign turned in too few signatures to qualify.

The 10 voters told KMGH (http://tinyurl.com/jmrs8rw ) that they didn’t sign for Keyser. The forgeries would not, by themselves, disqualify him.

“Here’s the important thing: I’m on the ballot and I’m going to beat Michael Bennet,” Keyser said when asked at the forum if he knew signatures had been forged. He gave similar “I’m on the ballot” responses to several follow-up questions.

Keyser also refused to answer repeated questions by KMGH about what he would say to those voters who said their signatures had been forged.

“There are people like you that have done the Democrats’ work who have spent hundreds of hours on this,” he told reporter Marshall Zellinger.

Keyser spokesman Matt Connelly said he had nothing more to add to Keyser’s remarks.

Keyser backers note the reports began with Progress Now, a liberal activist group. The group found one voter whose signature appeared in a Keyser petition but denied signing it.

Keyser is an Air Force Reserve officer who served in Afghanistan and Iraq. He was elected to the state House before resigning to seek the Republican Senate nomination, and he has stressed his national security credentials in his campaign.

Thursday’s developments were the latest in the campaign in which three candidates had to go to court to get to the primary. The others are Colorado Springs businessman Robert Blaha and former Aurora city councilman Ryan Frazier.

Frazier’s name is on the ballot provisionally while he appeals to Colorado’s Supreme Court about his own disqualification for too few signatures.

Graham, a former Colorado State University athletic director, petitioned onto the primary without incident. El Paso County Commissioner Daryl Glenn was overwhelmingly voted to the primary at the state GOP convention in March.

Progress Now asked two district attorneys whose jurisdiction includes the 10 voters’ addresses to investigate. There was no word of any investigation late Thursday.

The secretary of state’s office has said it was looking into whether there are any other forged signatures.